Impact of Red Blood Cells on Function and Metabolism of Porcine Deceased Donor Kidneys During Normothermic Machine Perfusion.

BACKGROUND: Normothermic machine perfusion (NMP) protocols using blood-based solutions are commonly used in the assessment of kidneys before transplantation. This procedure is, nevertheless, limited by blood availability and warrants the search for alternatives. We compared a blood-based solution with a serum-like preservation solution (Aqix) enriched with colloids with and without red blood cells (RBCs). METHODS: Porcine kidneys retrieved from an abattoir were subjected to 30 min of warm ischemia, followed by 3 h of hypothermic oxygenated machine perfusion at 4 °C. Subsequently, kidneys (n = 6 per group) were evaluated with NMP for 4 h with 5 different solutions: diluted blood, Aqix with BSA ± RBCs, or Aqix with dextran 40 ± RBCs. RESULTS: Throughout NMP, markers of renal function and tubular metabolism were favorable in groups with RBCs. The addition of RBCs resulted in 4- to 6-fold higher oxygen consumption rates. Controls had significantly higher ATP levels post-NMP, exhibited decreased production of oxidative stress markers, and had the highest creatinine clearance. In conclusion, this study shows that the addition of RBCs during NMP reduced renal injury, improved function, and was associated with increased renal metabolism. CONCLUSIONS: Although the RBC-BSA-supplemented Aqix solution was also able to support metabolism and renal function, a blood-based perfusion solution remains superior.

No more hypoglycaemia on days with physical activity and unrestricted diet when using a closed-loop system for 12 weeks: A post hoc secondary analysis of the multicentre, randomized controlled Diabeloop WP7 trial.

A post hoc analysis of the Diabeloop WP7 multicentre, randomized controlled trial was performed to investigate the efficacy of the Diabeloop Generation-1 (DBLG1) closed-loop system in controlling the hypoglycaemia induced by physical activity (PA) in real-life conditions. Glycaemic outcomes were compared between days with and without PA in 56 patients with type 1 diabetes (T1D) using DBLG1 for 12 weeks. After the patient announces a PA, DBLG1 reduces insulin delivery and, if necessary, calculates the amount of preventive carbohydrates (CHO). Daily time spent in the interstitial glucose range less than 70 mg/dL was not significantly different between days with and without PA (2.0% ± 1.5% vs. 2.2% ± 1.1%), regardless of the intensity or duration of the PA. Preventive CHO intake recommended by the system was significantly higher in days with PA (41.1 ± 35.5 vs. 21.8 ± 28.5 g/day; P < .0001), and insulin delivery was significantly lower (31.5 ± 10.5 vs. 34.0 ± 10.5 U/day; P < .0001). The time spent in hyperglycaemia and the glycaemic variation coefficient increased significantly on days with PA. In real-life conditions, the use of DBLG1 avoids PA-induced hypoglycaemia. Insulin adjustments and preventive CHO recommendation may explain this therapeutic benefit.

Oxidative Stress Evaluation in Ischemia Reperfusion Models: Characteristics, Limits and Perspectives.

Ischemia reperfusion injury is a complex process consisting of a seemingly chaotic but actually organized and compartmentalized shutdown of cell function, of which oxidative stress is a key component. Studying oxidative stress, which results in an imbalance between reactive oxygen species (ROS) production and antioxidant defense activity, is a multi-faceted issue, particularly considering the double function of ROS, assuming roles as physiological intracellular signals and as mediators of cellular component damage. Herein, we propose a comprehensive overview of the tools available to explore oxidative stress, particularly in the study of ischemia reperfusion. Applying chemistry as well as biology, we present the different models currently developed to study oxidative stress, spanning the vitro and the silico, discussing the advantages and the drawbacks of each set-up, including the issues relating to the use of in vitro hypoxia as a surrogate for ischemia. Having identified the limitations of historical models, we shall study new paradigms, including the use of stem cell-derived organoids, as a bridge between the in vitro and the in vivo comprising 3D intercellular interactions in vivo and versatile pathway investigations in vitro. We shall conclude this review by distancing ourselves from "wet" biology and reviewing the in silico, computer-based, mathematical modeling, and numerical simulation options: (a) molecular modeling with quantum chemistry and molecular dynamic algorithms, which facilitates the study of molecule-to-molecule interactions, and the integration of a compound in a dynamic environment (the plasma membrane...); (b) integrative systemic models, which can include many facets of complex mechanisms such as oxidative stress or ischemia reperfusion and help to formulate integrated predictions and to enhance understanding of dynamic interaction between pathways.

Efficacy of the Diabeloop closed-loop system to improve glycaemic control in patients with type 1 diabetes exposed to gastronomic dinners or to sustained physical exercise.

AIMS: To compare closed-loop (CL) and open-loop (OL) systems for glycaemic control in patients with type 1 diabetes (T1D) exposed to real-life challenging situations (gastronomic dinners or sustained physical exercise). METHODS: Thirty-eight adult patients with T1D were included in a three-armed randomized pilot trial (Diabeloop WP6.2 trial) comparing glucose control using a CL system with use of an OL device during two crossover 72-hour periods in one of the three following situations: large (gastronomic) dinners; sustained and repeated bouts of physical exercise (with uncontrolled food intake); or control (rest conditions). Outcomes included time in spent in the glucose ranges of 4.4-7.8 mmol/L and 3.9-10.0 mmol/L, and time in hypo- and hyperglycaemia. RESULTS: Time spent overnight in the tight range of 4.4 to 7.8 mmol/L was longer with CL (mean values: 63.2% vs 40.9% with OL; P ≤ .0001). Time spent during the day in the range of 3.9 to 10.0 mmol/L was also longer with CL (79.4% vs 64.1% with OL; P ≤ .0001). Participants using the CL system spent less time during the day with hyperglycaemic excursions (glucose >10.0 mmol/L) compared to those using an OL system (17.9% vs 31.9%; P ≤ .0001), and the proportions of time spent during the day with hyperglycaemic excursions of those using the CL system in the gastronomic dinner and physical exercise subgroups were of similar magnitude to those in the control subgroup (18.1 ± 6.3%, 17.2 ± 8.1% and 18.4 ± 12.5%, respectively). Finally, times spent in hypoglycaemia were short and not significantly different among the groups. CONCLUSIONS: The Diabeloop CL system is superior to OL devices in reducing hyperglycaemic excursions in patients with T1D exposed to gastronomic dinners, or exposed to physical exercise followed by uncontrolled food and carbohydrate intake.

A Computer Model of Oxygen Dynamics in the Cortex of the Rat Kidney at the Cell-Tissue Level.

The renal cortex drives renal function. Hypoxia/reoxygenation are primary factors in ischemia-reperfusion (IR) injuries, but renal oxygenation per se is complex and awaits full elucidation. Few mathematical models address this issue: none captures cortical tissue heterogeneity. Using agent-based modeling, we develop the first model of cortical oxygenation at the cell-tissue level (RCM), based on first principles and careful bibliographical analysis. Entirely parameterized with Rat data, RCM is a morphometrically equivalent 2D-slice of cortical tissue, featuring peritubular capillaries (PTC), tubules and interstitium. It implements hemoglobin/O2 binding-release, oxygen diffusion, and consumption, as well as capillary and tubular flows. Inputs are renal blood flow RBF and PO2 feeds; output is average tissue PO2 (tPO2). After verification and sensitivity analysis, RCM was validated at steady-state (tPO2 37.7 ± 2.2 vs. 36.9 ± 6 mmHg) and under transients (ischemic oxygen half-time: 4.5 ± 2.5 vs. 2.3 ± 0.5 s in situ). Simulations confirm that PO2 is largely independent of RBF, except at low values. They suggest that, at least in the proximal tubule, the luminal flow dominantly contributes to oxygen delivery, while the contribution of capillaries increases under partial ischemia. Before addressing IR-induced injuries, upcoming developments include ATP production, adaptation to minutes-hours scale, and segmental and regional specification.

Influence of Hypoxic Preservation Temperature on Endothelial Cells and Kidney Integrity.

Ischemia-reperfusion (IR) injury is unavoidable during organ transplantation and impacts graft quality. New paradigms are emerging including preservation at higher temperature than "hypothermia" or "cold": although 4°C remains largely used for kidney preservation, recent studies challenged this choice. We and others hypothesized that a higher preservation temperature, closer to physiological regimen, could improve organ quality. For this purpose, we used an in vitro model of endothelial cells exposed to hypoxia-reoxygenation sequence (mimicking IR) and an ex vivo ischemic pig kidneys static storage model. In vitro, 19°C, 27°C, and 32°C provided protection against injuries versus 4°C, by reducing cell death, mitochondrial dysfunction, leukocyte adhesion, and inflammation. However, ex vivo, the benefits of 19°C or 32°C were limited, showing similar levels of tissue preservation damage. Ex vivo 4°C-preserved kidneys displayed a trend towards reduced damage, including apoptosis. Macrophage infiltration, tubulitis, and necrosis were increased in the 19°C and 32°C versus 4°C preserved kidneys. Thus, despite a trend for an advantage of subnormothermia as preservation temperature, our in vitro and ex vivo models bring different insights in terms of preservation temperature effect. This study suggests that temperature optimization for kidney preservation will require thorough investigation, combining the use of complementary relevant models and the design of elaborated preservation solution and new technologies.

Pharmacotherapeutic approaches to treating depression during the perimenopause.

Introduction: Although postnatal depression is now well recognized, there is also a risk of depressive symptoms during perimenopause. The mechanisms underlying perimenopausal depression are still poorly understood; however, there are available treatment options. Areas covered: This review describes: the current pharmacotherapeutic approaches for perimenopausal depression, their strengths and weakness, and provides recommendations on how current treatment can be improved in the future. An electronic search identified specific guidelines for the treatment of perimenopausal depression released in 2018, as well as recent clinical studies on the subject. Expert opinion: The 2018 guidelines recommend selective serotonin reuptake inhibitors (SSRIs) and serotonin and noradrenaline reuptake inhibitors (SNRIs) as front-line medications for perimenopausal depression, but SSRIs and SNRIs are not always effective. The efficacy of estrogen in perimenopausal depression is well documented, but estrogen is not FDA-approved to treat mood disturbances in perimenopausal women. Clinical practice guidelines currently recommend to restrict hormone therapy to the symptomatic treatment of menopause (not for the prevention of chronic diseases). Research with new estrogenic compounds is under way to improve their benefit/risk ratio in perimenopausal depression.

Oxygen Consumption by Warm Ischemia-Injured Porcine Kidneys in Hypothermic Static and Machine Preservation.

Static cold storage (SCS) and hypothermic machine perfusion (HMP) are currently standard methods for renal grafts clinical preservation. Both methods are predominantly implemented without the active delivery of oxygen, even for donation after circulatory death-like kidneys. However, even under severe hypothermia (4°C-6°C), kidneys can consume oxygen and produce ATP. What is not established, though, is to what extent and how SCS and HMP compare in terms of oxygen. Using a porcine preclinical model of renal warm ischemia (WI) to compare SCS and HMP methods, we continuously monitored and quantified oxygen level and consumption along preservation; we also determined prepreservation and postpreservation cortical ATP level; values were given as median and [min; max] range. One-hour WI reduced ATP by ∼90% (from 3.3 [1.7; 4.5] mmol/L tissue in Controls). Oxygen consumption (QO2, µmol/min per 100 g) was determined from initial solution PO2 decrease (SCS and HMP) and from arterio-venous difference (HMP). In SCS and HMP, PO2 decreased rapidly (t1/2 ∼1 h) from atmospheric levels to 52.9 [38.0; 65.9] and 8.2 [3.0, 16.0] mmHg, respectively. In HMP, QO2 was 2.7 [0.4; 3.9] versus 0.5 [0.0; 1.3] in SCS (P < 0.05); postpreservation ATP amounted to 5.8 [3.2; 6.5] in HMP versus 0.1 [0.0; 0.2] in SCS. Despite hypothermic conditions in SCS or HMP, donation after circulatory death-like renal grafts require oxygen. Increased oxygen consumption, restored ATP level, and improved histological profile in HMP might explain the established HMP superiority over SCS. These results establish a rational basis for the use of oxygen in hypothermic preservation. Optimal levels required for preservation and graft-type variants remain to be determined.

Effects of Oxygen During Long-term Hypothermic Machine Perfusion in a Porcine Model of Kidney Donation After Circulatory Death.

BACKGROUND: Hypothermic machine perfusion (HMP) has become standard care in many center's to preserve kidneys donated after circulatory death (DCD). Despite a significant reduction in metabolism at low temperatures, the remaining cellular activity requires oxygen. Because of the role and safety of oxygen during HMP has not been fully clarified, its supply during HMP is not standard yet. This study investigates the effect of administering oxygen during HMP on renal function in a porcine DCD model. METHODS: After 30 minutes of warm ischemia, porcine slaughterhouse kidneys were preserved for 24 hours by means of cold storage (CS), or HMP with Belzer Machine Perfusion Solution supplemented with no oxygen, 21% or 100% oxygen. Next, kidneys were reperfused for 4 hours in a normothermic machine perfusion setup. RESULTS: HMP resulted in significantly better kidney function during normothermic machine perfusion. Thiobarbituric acid-reactive substances, markers of oxidative stress, were significantly lower in HMP preserved kidneys. HMP preserved kidneys showed significantly lower aspartate aminotransferase and lactate dehydrogenase levels compared with kidneys preserved by CS. No differences were found between the HMP groups subjected to different oxygen concentrations. Adenosine triphosphate levels significantly improved during HMP when active oxygenation was applied. CONCLUSIONS: This study showed that preservation of DCD kidneys with HMP is superior to CS. Although the addition of oxygen to HMP did not result in significantly improved renal function, beneficial effects were found in terms of reduced oxidative stress and energy status. Oxygen addition proofed to be safe and did not show detrimental effects.

Efficacy of the natural oxygen transporter HEMO2 life® in cold preservation in a preclinical porcine model of donation after cardiac death.

The growing use of marginal organs for transplantation pushes current preservation methods toward their limits, and the need for improvement is pressing. We previously demonstrated the benefits of M101, a natural extracellular oxygen carrier compatible with hypothermia, for the preservation of healthy renal grafts in a porcine model of autotransplantation. Herein, we use a variant of this preclinical model to evaluate M101 potential benefits both in static cold storage (CS) and in machine perfusion (MP) preservation in the transplantation outcomes for marginal kidneys. In the CS arm, despite the absence of obvious benefits within the first 2 weeks of follow-up, M101 dose-dependently improved long-term function, normalizing creatininemia after 1 and 3 months. In the MP arm, M101 improved short- and long-term functional outcomes as well as tissue integrity. Importantly, we provide evidence for the additivity of MP and M101 functional effects, showing that the addition of the compound further improves organ preservation, by reducing short-term function loss, with no loss of function or tissue integrity recorded throughout the follow-up. Extending previous observations with healthy kidneys, the present results point at the M101 oxygen carrier as a viable strategy to improve current organ preservation methods in marginal organ transplantation.

Cold flush after dynamic liver preservation protects against ischemic changes upon reperfusion - an experimental study.

Ex vivo machine perfusion of the liver after cold storage has found to be most effective if combined with controlled oxygenated rewarming up to (sub)-normothermia. On disconnection of the warm graft from the machine, most surgeons usually perform a cold flush of the organ as protection against the second warm ischemia incurred upon implantation. Experimental evidence, however, is lacking and protective effect of deep hypothermia has been challenged for limited periods of liver ischemia in other models. A first systematic test was carried out on porcine livers, excised 30 min after cardiac arrest, subjected to 18 h of cold storage in UW and then machine perfused for 90 min with Aqix-RSI solution. During machine perfusion, livers were gradually rewarmed up to 20 °C. One group (n = 6) was then reflushed with 4 °C cold Belzer UW solution whereas the second group (n = 6) remained without cold flush. All livers were exposed to 45 min warm ischemia at room temperature to simulate the surgical implantation period. Organ function was evaluated in an established reperfusion model using diluted autologous blood. Cold reflush after disconnection from the machine resulted in a significant increase in bile production upon blood reperfusion, along with a significant reduction in transaminases release alanine aminotransferase and of the intramitochondrial enzyme glutamate dehydrogenase. Interestingly, free radical-mediated lipid peroxidation was also found significantly lower after cold reflush. No differences between the groups could be evidenced concerning histological injury and recovery of hepatic energy metabolism (tissue content of adenosine triphosphate). Post-machine preservation cold reflush seems to be beneficial in this particular setting, even if the organs are warmed up only to 20 °C, without notion of adverse effects, and should therefore be implemented in the protocol.

Dynamic transcriptomic analysis of Ischemic Injury in a Porcine Pre-Clinical Model mimicking Donors Deceased after Circulatory Death.

Due to organ shortage, clinicians are prone to consider alternative type of organ donors among them donors deceased after circulatory death (DCD). However, especially using these organs which are more prone to graft dysfunction, there is a need to better understand mechanistic events ocuring during ischemia phase and leading to ischemia/reperfusion injuries (IRI). The aim of this study is to provide a dynamic transcriptomic analysis of preclinical porcine model kidneys subjected to ischemic stress mimicking DCD donor. We compared cortex and corticomedullary junction (CMJ) tissues from porcine kidneys submitted to 60 min warm ischemia (WI) followed by 0, 6 or 24 hours of cold storage in University of Wisconsin solution versus control non-ischemic kidneys (n = 5 per group). 29 cortex genes and 113 CMJ genes were significantly up or down-regulated after WI versus healthy kidneys, and up to 400 genes were regulated after WI followed by 6 or 24 hours of cold storage (p < 0.05). Functionnal enrichment analysis (home selected gene kinetic classification, Gene-ontology-biological processes and Gene-ontology-molecular-function) revealed relevant genes implication during WI and cold storage. We uncovered targets which we will further validate as biomarkers and new therapeutic targets to optimize graft kidney quality before transplantation and improve whole transplantation outcome.

Renal auto-transplantation promotes cortical microvascular network remodeling in a preclinical porcine model.

The vascular network is a major target of ischemia-reperfusion, but has been poorly investigated in renal transplantation. The aim of this study was to characterize the remodeling of the renal vascular network that follows ischemia-reperfusion along with the most highly affected cortex section in a preclinical renal transplantation model. There were two experimental groups. The first was a grafted kidney group consisting of large white pigs for which the left kidney was harvested, cold flushed, preserved for 24 h in the University of Wisconsin's preservation solution, and then auto-transplanted (n = 5); the right kidney was removed to mimic the situation of human kidney transplantation. The second group (uni-nephrectomized kidney group) consisted of animals that underwent only right nephrectomy, but not left renal transplantation (n = 5). Three months after autotransplantation, the kidneys were studied by X-ray microcomputed tomography. Vessel morphology and density and tortuosity of the network were analyzed using a 3D image analysis method. Cortical blood flow was determined by laser doppler analysis and renal function and tissue injury assessed by plasma creatinine levels and histological analysis. Renal ischemia-reperfusion led to decreased vascular segment volume associated with fewer vessels of less than 30 µm, particularly in the inner cortex:0.79 ± 0.54% in grafted kidneys vs. 7.06 ± 1.44% in uni-nephrectomized kidneys, p < 0.05. Vessels showed higher connectivity throughout the cortex (the arborescence factor of the whole cortex was less in grafted than uni-nephrectomized kidneys 0.90 ± 0.04 vs. 1.07 ± 0.05, p < 0.05, with an increase in the number of bifurcations). Furthermore, cortical blood flow decreased early in kidney grafts and remained low three months after auto-transplantation. The decrease in microvasculature correlated with a deterioration of renal function, proteinuria, and tubular dysfunction, and was associated with the development of fibrous tissue. This work provides new evidence concerning the impact of ischemia-reperfusion injuries on the spectrum of renal vascular diseases and could potentially guide future therapy to preserve microvessels in transplantation ischemia-reperfusion injury.

Polynomial algebra reveals diverging roles of the unfolded protein response in endothelial cells during ischemia-reperfusion injury.

The unfolded protein response (UPR)--the endoplasmic reticulum stress response--is found in various pathologies including ischemia-reperfusion injury (IRI). However, its role during IRI is still unclear. Here, by combining two different bioinformatical methods--a method based on ordinary differential equations (Time Series Network Inference) and an algebraic method (probabilistic polynomial dynamical systems)--we identified the IRE1α-XBP1 and the ATF6 pathways as the main UPR effectors involved in cell's adaptation to IRI. We validated these findings experimentally by assessing the impact of their knock-out and knock-down on cell survival during IRI.

Integration of detailed modules in a core model of body fluid homeostasis and blood pressure regulation.

This paper presents a contribution to the definition of the interfaces required to perform heterogeneous model integration in the context of integrative physiology. A formalization of the model integration problem is proposed and a coupling method is presented. The extension of the classic Guyton model, a multi-organ, integrated systems model of blood pressure regulation, is used as an example of the application of the proposed method. To this end, the Guyton model has been restructured, extensive sensitivity analyses have been performed, and appropriate transformations have been applied to replace a subset of its constituting modules by integrating a pulsatile heart and an updated representation of the renin-angiotensin system. Simulation results of the extended integrated model are presented and the impacts of their integration within the original model are evaluated.

A computational model of the circulating renin-angiotensin system and blood pressure regulation.

UNLABELLED: The renin-angiotensin system (RAS) is critical in sodium and blood pressure (BP) regulation, and in cardiovascular-renal (CVR) diseases and therapeutics. As a contribution to SAPHIR project, we present a realistic computer model of renin production and circulating RAS, integrated into Guyton's circulatory model (GCM). Juxtaglomerular apparatus, JGA, and Plasma modules were implemented in C ++/M2SL (Multi-formalism Multi-resolution Simulation Library) for fusion with GCM. Matlab optimization toolboxes were used for parameter identification. In JGA, renin production and granular cells recruitment (GCR) are controlled by perfusion pressure (PP), macula densa (MD), angiotensin II (Ang II), and renal sympathetic activity (RSNA). In Plasma, renin and ACE (angiotensin-converting enzyme) activities are integrated to yield Ang I and II. Model vs. data deviation is given as normalized root mean squared error (nRMSE; n points). IDENTIFICATION: JGA and Plasma parameters were identified against selected experimental data. After fusion with GCM: (1) GCR parameters were identified against Laragh's PRA-natriuresis nomogram; (2) Renin production parameters were identified against two sets of data ([renin] transients vs. ACE or renin inhibition). Finally, GCR parameters were re-identified vs. Laragh's nomogram (nRMSE 8%, n = 9). VALIDATION: (1) model BP, PRA and [Ang II] are within reported ranges, and respond physiologically to sodium intake; (2) short-term Ang II infusion induces reported rise in BP and PRA. The modeled circulating RAS, in interaction with an integrated CVR, exhibits a realistic response to BP control maneuvers. This construction will allow for modelling hypertensive and CVR patients, including salt-sensitivity, polymorphisms, and pharmacotherapeutics.

SAPHIR: a physiome core model of body fluid homeostasis and blood pressure regulation.

We present the current state of the development of the SAPHIR project (a Systems Approach for PHysiological Integration of Renal, cardiac and respiratory function). The aim is to provide an open-source multi-resolution modelling environment that will permit, at a practical level, a plug-and-play construction of integrated systems models using lumped-parameter components at the organ/tissue level while also allowing focus on cellular- or molecular-level detailed sub-models embedded in the larger core model. Thus, an in silico exploration of gene-to-organ-to-organism scenarios will be possible, while keeping computation time manageable. As a first prototype implementation in this environment, we describe a core model of human physiology targeting the short- and long-term regulation of blood pressure, body fluids and homeostasis of the major solutes. In tandem with the development of the core models, the project involves database implementation and ontology development.

The double nucleation model for sickle cell haemoglobin polymerization: full integration and comparison with experimental data.

Sickle cell haemoglobin (HbS) polymerization reduces erythrocyte deformability, causing deleterous vaso-occlusions. The double-nucleation model states that polymers grow from HbS aggregates, the nuclei, (i) in solution (homogeneous nucleation), (ii) onto existing polymers (heterogeneous nucleation). When linearized at initial HbS concentration, this model predicts early polymerization and its characteristic delay-time (Ferrone et al. J Mol Biol 183(4):591-610, 611-631, 1985). Addressing its relevance for describing complete polymerization, we constructed the full, non-linearized model (Simulink), The MathWorks). Here, we compare the simulated outputs to experimental progress curves (n = 6-8 different [HbS], 3-6 mM range, from Ferrone's group). Within 10% from start, average root mean square (rms) deviation between simulated and experimental curves is 0.04 +/- 0.01 (25 degrees C, n = 8; mean +/- standard error). Conversely, for complete progress curves, averaged rms is 0.48 +/- 0.04. This figure is improved to 0.13 +/- 0.01 by adjusting heterogeneous pathway parameters (p < 0.01): the nucleus stability (sigma(2) micro( cc ): + 40%), and the fraction of polymer surface available for nucleation (phi), from 5e(-7), (3 mM) to 13 (6 mM). Similar results are obtained at 37 degrees C. We conclude that the physico-chemical description of heterogeneous nucleation warrants refinements in order to capture the whole HbS polymerization process.

Dynamic simulation of mitochondrial respiration and oxidative phosphorylation: comparison with experimental results.

Hypoxia hampers ATP production and threatens cell survival. Since cellular energetics tightly controls cell responses and fate, ATP levels and dynamics are of utmost importance. An integrated mathematical model of ATP synthesis by the mitochondrial oxidative phosphorylation/electron transfer chain system has been recently published (Beard, PLoS Comput Biol 1(4):e36, 2005). This model was validated under static conditions. To evaluate its performance under dynamical situations, we implemented and simulated it (Simulink), The Mathworks). Inner membrane potential (DeltaPsi) and [NADH] (feeding the electron transfer chain) were used as indicators of mitochondrial function. Root mean squared error (rmse) was used to compare simulations and experiments (isolated cardiac mitochondria, Bose et al. J Biol Chem 278(40):39155-39165, 2003). Steady-state experimental data were reproduced within 2-6%. Model dynamics were evaluated under: (i) baseline, (ii) activation of NADH production, (iii) addition of ADP, (iv) addition of inorganic phosphate, (v) oxygen exhaustion. In all phases, except the last one, DeltaPsi and [NADH] as well as oxygen consumption, were reproduced (within 10, 7 and 12%, respectively). Under anoxia, simulated DeltaPsi markedly depolarized (no change in experiments). In conclusion, the model reproduces dynamic data as long as oxygen is present. Anticipated improvement by the inclusion of ATP consumption and explicit Krebs cycle are under evaluation.

SAPHIR - a multi-scale, multi-resolution modeling environment targeting blood pressure regulation and fluid homeostasis.

We present progress on a comprehensive, modular, interactive modeling environment centered on overall regulation of blood pressure and body fluid homeostasis. We call the project SAPHIR, for "a Systems Approach for PHysiological Integration of Renal, cardiac, and respiratory functions". The project uses state-of-the-art multi-scale simulation methods. The basic core model will give succinct input-output (reduced-dimension) descriptions of all relevant organ systems and regulatory processes, and it will be modular, multi-resolution, and extensible, in the sense that detailed submodules of any process(es) can be "plugged-in" to the basic model in order to explore, eg. system-level implications of local perturbations. The goal is to keep the basic core model compact enough to insure fast execution time (in view of eventual use in the clinic) and yet to allow elaborate detailed modules of target tissues or organs in order to focus on the problem area while maintaining the system-level regulatory compensations.